1. Field of the Invention
The present invention relates to a ceramic heater, a heater electrode, and a method for manufacturing a ceramic heater.
2. Description of the Related Art
One known ceramic heater for heating semiconductor wafers is a sintered alumina disc having an embedded heater electrode. For example, Patent Literature 1 discloses a method for manufacturing a ceramic heater, including preparing two compacts having a predetermined shape from a mixed powder of alumina and magnesium fluoride, applying a paste for a heater electrode to one of the compacts and then placing the other compact thereon, and firing the laminate at a low firing temperature in the range of 1120° C. to 1300° C. In a process of manufacturing a ceramic heater, use of WC as a paste in high-temperature firing at 1700° C. results in sufficient sintering of WC and electrical characteristics suitable for a heater electrode. However, in low-temperature firing at a temperature in the range of 1120° C. to 1300° C., use of WC as a paste results in considerable falling of particles, making electrical resistance measurement impossible, and use of a mixed powder of WC and alumina as a paste results in insufficient densification of the resulting electrode and poor electrical characteristics (Comparative Examples 21 and 22 in Patent Literature 1). Thus, a mixed powder of WC, Ni, and alumina is used as a paste in Patent Literature 1.